The invention relates to a cleanable scraper station.
A cleanable scraper station of the type indicated is known from the marketing and shop drawings of a manufacturer and supplier of cleanable pipeline systems; these printed publications have been made available only to a limited number of users but not to the public at large.
Both product and, in the case of flush cleaning, a cleaning means flows through the state-of-the-art scraper station; as a result of the prescribed immobilization of the scraper in the scraper station, contact surfaces are formed between scraper and scraper housing which are not accessible for adequate cleaning during flushing.
To this extent it exhibits the cleaning process disadvantages of another state-of-art cleanable scraper station (WO-A-91/17386); product does not flow around the latter during its travel, in contrast to the former, so that, especially in the processing of high-quality or hygienically especially sensitive products, the passage section of a T-branch facing the scraper station is not scrapeable for the purpose of recovering the product which has accumulated there. Although the reference does contain a statement to the effect that the dispatching or receiving station is connected directly to the product flow section by way of the transitional element of the T-branch, in each instance there nevertheless remains an area in which product losses occur and, on the other hand, in which the product stagnates during product flow, since this area cannot be sensed by the product flow as dead space.
Hence the invention is based on the problem of developing a generic scraper station so that its cleaning capacity during flushing is improved, uninterrupted cleaning of the entire surface of the scraper in particular being ensured.
The decisive difference between the scraper station claimed for the invention and that of the state of the art is that in a first embodiment the scraper is placed in its flow-around position by means of a controllable second stop in conjunction with the movable first stop. The positioning is designed so that the scraper is separated by adequate clearance from the components bounding it on all sides, that is, so that the scraper possesses limited mobility on all sides. In an alternative second embodiment the scraper is additionally positively locked in a screen cage guard which is connected to the movable first stop. An alternative third embodiment provides that the scraper be placed in its flow-around position exclusively by means of a screen cage guard connected to the movable first stop in its flow-around position.
The screen cage guard mounted on the movable first stop, which guard consists in one preferred embodiment claimed for the invention of at least two U-shaped elements which, as viewed axially outward, form an insertion opening, an opening narrowed relative to the latter, and a radially widening grip opening, imparts additional advantages to the cleanable scraper station. Firstly, the scraper can be gripped securely, even in the vertical inlet direction of movement against the force of gravity in the enlarged cross-section, and moved from its closed position to its flow-around position in the enlarged cross-section. This is ensured by positive-locking retention of the scraper between at least three U-shaped elements. In addition, the positive locking retention of the scraper may be designed so that the scraper cannot free itself from its positive locking retention. In this case the controllable second stop may be dispensed with. The positive-locking retention of the scraper is overcome only if the scraper is transferred by the screen cage guard to its locked position and then forced from the guard by the product impinging on it and into the cleanable pipeline section adjoining it. Another advantage of the positive locking retention of the scraper in the screen cage guard is that the scraper can easily be removed from the opened scraper station by means of this positive locking.
In order to be able to clean the scraper on all sides by flushing, an especially advantageous development of the scraper station claimed for the invention provides a stationary stop that delimits the location of the scraper in its flow-around position in the enlarged cross-section if, after movement of the movable first stop by a partial travel distance length T1 from the end position of the movable first stop or of the screen cage guard determining immobilization of the scraper in its flow-around position in the enlarged cross-section, a controllable second stop makes movement of the scraper away from its location possible. As a result of this measure, the contact surface between the scraper and the movable first stop may be freed so that cleaning means may be applied to this surface of the scraper otherwise covered by the stop (this is the frontal surface in the exemplary embodiment).
Optimum cleaning conditions for the scraper are created if, as is provided by another design of the scraper station claimed for the invention, the scraper comes to rest outside its contact area with the movable first stop or with the screen cage guard. It has been found to be advantageous for the stationary stop to be annular in form and to have a central passage, so that cleaning means, and if desired, product as well, can flow through the scraper station on the way through this central passage. For one thing, this flow control ensures efficient and symmetrical flow around the scraper, and for another flow losses due to the stationary stop are reduced to a tolerable level.
In a second embodiment particular advantages are presented by design of the stationary stop in the form of two U-shaped elements which are mounted in reciprocal diametrical and radial symmetry and are convex in shape in the area of their contact surface with the scraper. This design reduces the contact surface with the scraper to the absolutely necessary minimum.
In the case of high-quality or hygienically sensitive products, another advantageous embodiment of the scraper station claimed for the invention provides that the quantity of product in the scraper station not involved in the scraping process be reduced by mounting the connection for the pipeline section directly on the duct of the movable first stop. It is also advantageous for the interior of the scraper station in the area of the connection in question to be designed so as to be free of dead space, by having an interior profile conforming to the flow, that is, one which conforms to the streamline pattern during free flow through the scraper station. These interior adaptations also make certain that no amounts of product will stagnate in the area of the duct as the product travels through the passage in the movable first stop.
Flow around the scraper in the enlarged section is in another embodiment of the scraper station claimed for the invention ensured by providing at least three spacers which keep the scraper a certain distance from a housing of the scraper station circumferentially in the area of the enlarged cross-section. It has been found expedient to design the spacers in the form of cylindrical rods which enclose the scraper on all sides as a cage, with clearance, and which are especially easy to clean during flushing.
In order to move the scraper from its flow-around position to its locked position, another embodiment of the scraper station claimed for the invention provides a movable first stop which it is expedient to design as an adjusting rod, which engages the scraper station on the fly in the direction of movement by means of a first drive. The frontal surface of the adjusting rod becomes a stopper for the scraper when the scraper station operates as a receiving station.
In order to ensure the movements of the movable first stop required for optimum control of cleaning means in the scraper station, another advantageous embodiment of the scraper station claimed for the invention provides that the first drive alternatively be activated by pressure means; as a result, firstly, the movable first stop can be transferred in one direction by a primary movement to an end position, one in which the scraper is situated in its flow-around position in the enlarged cross-section and as a result, secondly, partial movement T1 may be executed against a spring in the first drive. While the movable first stop is moved to its initial position by the return spring after the partial movement T1 of the stop, return movement takes place following the primary movement as a result of application of pressure means to the piston in the opposite direction. Achievement of the pertinent end position before and after the primary movement is sensed by revertive communications devices which sense and report the pertinent position of the movable first stop.
The scraper is advantageously placed in its flow-around position in the enlarged cross-section in accordance with the alternative first embodiment by designing the controllable second stop as a retaining rod which is caused by a second drive to engage the scraper station transversely to the direction of movement of the scraper and the end of which facing away from the drive is seated in a thrust bearing in the housing of the scraper station. The twofold seating of the retaining rod makes certain that the scraper will not be bent or tilted by pressure forces acting on the scraper, ones which may press against the retaining rod.
A design which is better from the viewpoint of cleaning procedure is ensured by the alternative second embodiment in that the controllable second stop is made up of two lugs which are positioned in reciprocal diametrical and radial symmetry and each of which is introduced into its engaged position by a second drive at an angle smaller than 90 degrees, as measured relative to the direction of departure of the scraper from the scraper station, in the enlarged cross-section of the latter. This arrangement eliminates the thrust bearing of the retaining rod, which creates problems from the viewpoint of cleaning procedure, in that a special procedure must be followed in cleaning this bearing. Choice of a suitable angle at which the lugs engage the enlarged cross-section ensures that the pertinent retaining force applied to the rod will be no greater than that in the case of purely axial support.
Another expedient embodiment of the scraper station claimed for the invention provides in this connection that the second drive, when in the nonactivated state (at rest), will transfer the controllable second stop to the engaged position referred to above. When in the nonactivated position the scraper is accordingly positioned between the adjusting rod and the second stop (retaining rod or lugs). The scraper may be moved to its locked position only when the two drives are linked by control engineering means; in another expedient embodiment of the proposed scraper station, both the engaged position of the controllable second stop and its second end position, a released position, are sensed by a revertive communications device.
In order to be able to clean the controllable second stop in the area of its engagement in the thrust bearing in the housing as well, another embodiment of the scraper station claimed for the invention provides that this stop may be returned by means of its drive in the direction of the released position by a partial travel distance T2 from its engaged position in the thrust bearing in the housing in the direction of the released position.
In fully automatic systems in which the cleanable scraper station claimed for the invention is used, it is advantageous or often even absolutely necessary (see above discussion of the first drive) to provide revertive communication devices for sensing the position of the scraper in the scraper station. Revertive communication devices are provided in another advantageous embodiment of the proposed scraper station which sense at least the dispatch position or locked position and the flow-around position of the scraper.
In order to prevent undesirable pressure losses during flow through the scraper station, and especially during flow of product, provision is made such that both the second connection and the passage cross-section in the enlarged cross-section are provided with a cross-section which corresponds more or less to the passage cross-section of the scrapeable pipeline section.
In order to ensure danger-free disassembly of the cleanable scraper station, provision is made in another embodiment claimed for the invention such that the scraper station is provided, on a rod passage designed as a cover element with a safety lock operating essentially as a bayonet lock, this safety lock allowing opening of the scraper station only after the pressure in the latter has been reduced.